Shortened dynamic FDG-PET protocol to determine the glucose metabolic rate in non-small cell lung carcinoma

An important advantage of dynamic over static FDG-PET is the possibility to calculate tumor glucose metabolic rates (MRglu), as opposed to FDG uptake values only. One of the reasons why dynamic FDG-PET is not widely used in clinical practice is the relatively long scan time, necessary to obtain the conditions under which the linear approximation in the two-compartment model with trapping is valid (Patlak analysis). This study examined whether it is possible to shorten the standard data acquisition time lasting from 0 up to 50 min post injection, as used in our hospital, without significant alteration of the resulting MRglu values. Methods: Twenty-nine lesions in 16 dynamic FDG-PET scans of 50 min in 13 patients with non-small cell lung carcinoma were analyzed. Arterial sampling was used to obtain the blood plasma input function. Patlak analysis was applied to several time intervals of the same dynamic scan. These intervals were 10 – 50, 10 – 40, 10 – 30 and 10 – 20 min post injection, with effective scan durations of 50, 40, 30 and 20 min, respectively. In each analysis, tumor regions were determined in FDG uptake maps in the last time frame of the specific time interval using 3-dimensional isocontours at 50% of the maximum voxel value. Results: The mean MRglu values were 0.136 ± 0.066, 0.139 ± 0.070, 0.134 ± 0.072 and 0.163 ± 0.088 μmol/(mL×min) for the respective time intervals. High correlations (r2 = 0.972 and 0.956, respectively) were found between the full length 50 min scans and the shortened 40 and 30 min scans. MRglu values derived from the shortest 20 min scan, however, still correlated well (r2=0.886) with the 50 min scans, but were somewhat higher on average. Conclusion: A shortened data acquisition protocol of 30 min using Patlak analysis is sufficient to obtain tumor glucose metabolic rates which correlate well and show good agreement with a protocol of 50 min. These results are of importance for the clinical feasibility of dynamic FDG-PET.